The present invention relates to aqueous compositions of organic diazo compounds and to a method of modifying the surface of polymers utilizing the subject composition. Specifically, the present invention provides aqueous solutions of organic diazo compounds and to the use of said solutions to modify the chemical nature of the surface of polymeric substrates. The present invention is also directed to aqueous solutions of organic diazo compounds exhibiting storage stability.
The innumerable synthetic polymers which have been prepared, tested and reported in the literature reflect the continuing need to provide materials which have a unique combination of properties. In certain instances polymers have been synthesized in attempts to enhance one or more of their overall or macro properties, such as enhanced tensile strength, inertness to specific environments, porosity and the like. Polymers have been synthesized in attempts to enhance properties required at certain sites of the resultant polymer formation, i.e. surface properties, such as enhanced wettability, adhesion, solvent resistance, herbicidal or pharmaceutical activity and the like. In most instances, the formation of polymers which exhibit enhanced properties at specific sites is not practical or requires costly synthesis. Further, when formed, the newly synthesized polymer has less desirable overall properties than the original non-modified polymer. Thus, the modification of a known synthetic polymer to enhance or modify its properties frequently involves the sacrifice of other desirable properties and, at time, necessitates expensive and complicated procedures and formulations. When surface modification is desired, various methods have been utilized. The surface may be primed with a particular liquid to enhance the treated polymer surface adhesion, wettability or other desired properties. Polyolefins have been subjected to irradiation to enhance their ability to bond to themselves when subjected to heat and pressure in the presence of free radical generating compounds. Other methods of modifying surfaces of preformed polymer articles are well known and include surface degradation, swelling with weak solvents as well as introduction of reactive inorganic groups such as sulfonic, chlorine groups by subjecting the formed polymer article to reactive baths to cause reaction between the polymer article's surface and the reactive moiety. Each of these means of modifying the surface of a polymer article is cumbersome and is limited to a very small range of polymer substrates and modifying reactants. In addition, chemical modification of solid surfaces poses unique problems as compared to chemical reactions in solution or in dispersion. The solid surface is never entirely uniform, and the orientation of molecules at the solid surface is generally restricted, thus limiting their chemical reactivity, and solid surfaces are frequently contaminated with absorbed materials, such as carbon dioxide, water, oxygen, etc., which are frequently very difficult to remove. Atmospheric contamination of a solid surface can present a serious impurity problem in interfacial chemical reactions and can affect the course of the reaction. The reaction kinetics of free radicals in a homogeneous system, e.g. solution, are greatly different from the reaction kinetics of free radicals in a heterogeneous system, e.g. a solid surface. Since a solid surface differs from a solution in physical, thermodynamic and free energy characteristics, the field of chemical reactions involving solid surfaces has been under recent investigation as a separate and distinct discipline.
U.S. Pat. No. 3,376,278 teaches a means of modifying surface properties of polymers by contacting the surface of the polymer with a diazo compound and irradiating the interface between the diazo compound and the polymer surface with actinic radiation to cause the diazo compound to provide a divalent carbon species with the liberation of nitrogen. The teachings of U.S. Pat. No. 3,376,278 are incorporated herein by reference. The process provided for by this teaching is applicable to a wide variety of polymers and diazo compounds. The major criteria for the polymer is that it contain non-aromatic carbon-hydrogen bonds and for the diazo compound is that the diazo group be attached to a non-aromatic carbon atom. A further discussion of polymers and diazo compounds which can be used is given herein below.
The difficulty with the use of diazo compounds is their high propensity to spontaneously decompose. Such decomposition is normally catastrophic in nature. In order to provide some degree of stability, diazo compounds are normally required to be in the form of a solute in an organic solvent such as toluene, benzene, hexane, methylene chloride and the like but, even here, they require high degrees of dilution and, thus, the presence of high amounts of organic solvent is needed to provide a reasonably stable composition. When diazo compounds have been prepared in aqueous systems, they have been immediately removed from water and made part of an organic solution. It was commonly believed that water and diazo compounds would spontaneously react and, further, that the carbene dissociation product would also react with water to cause deactivation of the specie. The use of diazo compounds as a means of modifying polymeric articles has not found commercial favor because of the hazards normally associated with the diazo compound as well as environmental handling and processing problems associated with the use of large quantities of organic solvents. In addition, the use of organic solvents, in many applications (i.e. modification of food packaging material) requires careful removal of the solvent to avoid contaminating materials which are subsequently put in contact with the modified polymer. The use of organic solvents also presents the problems of contaminating the polymer surface and entrapping residual amounts of reaction by-products. If highly volatile solvents are used, they tend to evaporate, leaving a concentrate of diazo compound which can be hazardous.
It is highly desired and an object of the present invention to provide aqueous compositions in which at least one diazo compound is contained therein. It is further highly desired and an object of the present invention to have the composition substantially free of organic solvent. It is highly desirable and an object of the present invention to provide aqueous storage stable diazo compositions. Finally, it is highly desirable and an object of the present invention to provide aqueous diazo compositions such that the diazo compounds are readily activated to dissociate and react with polymeric substrates to modify them in a safe manner.